My Diesel Exhaust Fluid experience - 8/2011 X5 xDrive35d

[fullmetaljacket]

Originally Posted by josiahg52

You are correct that the system can't sense incorrect fluid. It's can monitor NOx emissions and if they remain high after several hundred kilometers even with normally adequate DEF injection rates, the error message and/or DTC is issued. Checking the NOx sensors is a good start. "NOx System Inefficiency" DTC is 004D16, FYI.

Thanks for the insights Josh! Now I did some more scanning using Foxwell NT510 to dig into the NOx sensor condition and found out the following:

1. NOX Concentration I (determination> 10 minutes driving!) 60.97 ppm

2. NOX Concentration II ( determination> 10 minutes driving!) -0.02 ppm

3. Status Signal NOX sensor I: Released NOX concentration can be read out

4. Status Signal NOX sensor II: 0

Does this actually mean that NOX sensor II is the culprit? Which one is sensor 2 and how do I locate this? Planning on doing more research on replacing the NOX sensor and hopeully I can DIY it...? Exciting!